1. Field of the Invention
The invention relates to a high voltage circuit interrupter of the high capacity fuse type, and more particularly to a sealing construction and method for assembling the sealing construction on the end of such a device.
2. Description of the Prior Art
High voltage expulsion fuses are current interrupter devices which are operated to open a circuit by means of expelling gases and metallic vapors at high velocity and pressure, which are created in extinguishing an arc initiated in the device by a fault current.
Circuit fuses, or interrupters of the type involved in this invention are disclosed in U.S. Pat. Nos. 2,590,524; 3,401,243; 3,401,244; 3,401,245; 3,401,246; and 3,855,563. These devices of these patents are generally sealed at both the upper and lower ends. The sealing at at least the end near the fuse element is generally accomplished by employing a vinyl cap which encloses the opening and which is affixed by an epoxy cement.
These devices of the prior art and that of the invention are generally used outdoors in utility systems, with high voltage loadings and possibly different current ratings. Regardless of the magnitude of the voltage loadings and the current ratings of these types of devices, it is desirable to provide an undamageable and effective seal at the end of the device near the fuse element. This seal has to endure atmospheric conditions where moisture leaking inside the fuse generally tends to cause the arc-extinguishing material to swell thereby restricting movement of the elongated rod.
Movement of this rod through the arc-extinguishing material is essential in order to extinguish the arc initiated by the melting of the fuse element at the end of the rod. The extinguishing action of the arc creates the gases and vapors in the device. At a low fault current interruption of the device relative to its rating, the internally generated gas and vapor pressures are low. At this low fault current level the seal must remain intact in order to allow enough gases and vapors to build up to effectively extinguish the arc. At high current interruptions of the device relative to its rating, the internally generated gas and vapor pressures are high and are developed at a high rate of speed. At this high fault current level the seal must be reliably and consistently rupturable so that excessive and disruptive pressures are not contained within the fuse resulting in an explosive condition. It is essential that the seal at the fuse end be capable of being blown off to vent these pressures.
One of the major drawbacks of the enclosure cap used at the end of the fuse to seal the present day devices is that this cap is affixed with varying amounts of epoxy cement. This method of assembling a seal at the end of the fuse may result in both an ineffective sealing condition and/or an intolerable condition in that the end is either plugged up preventing the escape of the pressures at the high fault current levels or the cap is detached prematurely from the fuse end at the low fault current levels.
There is a need therefore for an improved high voltage circuit interrupter or fuse of the expulsion type which maintains an effective sealing condition under normal current carrying operations or under a low fault current interruption, regardless of the atmospheric conditions, but which sealing condition is readily interrupted at a high fault current level which exceeds the maximum allowable loading value for the system.
More particularly, there is a need for an improved sealing construction and method for assembling such sealing construction for a high voltage circuit interrupter or fuse of the expulsion type, which sealing construction is reliably and consistently rupturable at high fault current levels.
There is a further need for such a circuit interrupter to have an hermetically and mechanically controlled seal which is consistently rupturable at high fault current levels so that excessive and disruptive gas and/or vapor pressures are not contained in the interrupter thereby presenting a detrimental explosive condition.